Will - You missed Dutch Uncle (somebody who's never there). In the 1600s we were at war with the Netherlands, I reckon that because this period was also one of increasing standardisation of the English language, some or all of these (negative) phrases got included in the broadsheets and passed into general use.

I've got an inkling that 'Dutch Courage' refers to the aftermath of the siege of Magdeburg, which resulted in 25000 civilian deaths or thereabouts, after the sacking soldiers got p*ssed and started hacking women and children to death.